1. Field of the Invention
The present invention relates to an inkjet recording head cartridge and an inkjet recording apparatus.
2. Description of the Prior Art
An inkjet recording head cartridge (hereinafter referred to as cartridge) mounted in the carriage of conventional inkjet recording apparatuses is constructed to supply ink to a supply orifice of a head (head chip) through an ink supply passage from an ink tank.
The cartridge thus constructed has problems in (1) processing for bubbles generated in the ink supply passage and the head and (2) control of the fluctuation of ink supply pressure within the ink supply passage and the head. Various proposals are made to solve these problems. Hereinafter, a description will be made of several of these proposals.
The following four examples are proposed as measures against (1).
According to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 6-218945 (hereinafter referred to as conventional example 1), upon detecting bubbles generated in an ink supply passage, recording operation is stopped to prevent the bubbles from invading into a recording head.
Also, according to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 9-226142 (hereinafter referred to as a conventional example 2), an ink supply passage having a smaller cross-sectional area than that of a recording head opening part is provided to increase an ink flow velocity and thereby increase the ability to eliminate bubbles.
Furthermore, according to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 9-277552 (hereinafter referred to as a conventional example 3), a filter provided in an ink flow passage is provided with a bubble discharge part which discharges bubbles by pressuring the ink flow passage toward the outside.
According to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 9-131890 (hereinafter referred to as a conventional example 4), a wall outlined along a manifold is provided to discharge bubbles upward without depositing them on the wall face.
On the other hand, the following four example are proposed as measures against (2).
According to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 5-31904 (hereinafter referred to as a conventional example 5), bubbles are formed within a common liquid chamber by heating, and pressure waves are absorbed by transforming the bubbles to restrain pressure fluctuation caused by ink injection.
Also, according to the invention disclosed in Japanese Published Unexamined Patent Application No. Sho 55-128465 (hereinafter referred to as a conventional example 6), a minute hole for communication between the ink liquid passage and air is provided in part of the ink liquid passage to restrain pressure fluctuation.
Furthermore, according to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 7-125234 (hereinafter referred to as a conventional example 7), a gas holding part and a subheater for changing the volume of gas are provided to restrain pressure fluctuation caused by ink injection by changing the natural frequency of an ink supply system.
Furthermore, according to the invention disclosed in Japanese Published Unexamined Patent Application No. Hei 9-136415 (hereinafter referred to as a conventional example 8), plural gas holding parts for holding gas therein are provided in an ink supply passage to absorb pressure oscillation.
There are the following problems in the conventional examples 1 to 4.
In the conventional example 1, a bubble detection unit is required and it is questionable whether satisfactory bubble detection precision is obtained. Also, if a bubble is detected, recording must be temporarily halted.
In the conventional example 2, although it is possible to decrease the frequency of bubble-induced printing defects to some degree, it is impossible to completely eliminate printing defects.
In the conventional example 3, a pressurizing system for discharging bubbles is required, so that the apparatus becomes complicated.
In the conventional example 4, discharged bubbles accumulate under a filter and, if the accumulated bubbles spread throughout the manifold, printing would be disabled.
There are the following problems in the conventional examples 5 to 8.
In the conventional example 5, a heating unit in addition to an emission heater is required in the common liquid chamber, so that the mechanism becomes very complicated. Also, it is very difficult to control the size of bubbles generated by the heating unit.
In the conventional example 6, ink evaporation from the minute hole for communication with air and ink hardening in the minute hole are problematic.
In the conventional example 7, a heating unit is additionally required, so that the mechanism becomes complicated. Also, bubble size control is difficult.
In the conventional example 8, gas holding parts must be created, and therefore the construction of the ink supply passage becomes complicated. Also, gas in the gas holding parts may replace ink in the course of long-term preservation.
As described above, the conventional examples 1 to 8 have the problems that the structure of the mechanism is complicated or conventional problems cannot be completely solved.
Therefore, the present invention provides an inkjet recording head cartridge and an inkjet recording apparatus that have a simple structure and high reliability.
According to an aspect of the present invention, the inkjet recording head cartridge includes individual flow passages each having an ink emission orifice at one end thereof and an ink inflow orifice at another end thereof, an ink supply chamber communicating with the ink inflow orifices, and a heater face provided to be orthogonal to an ink emission face on which the ink emission orifices are formed, the heater face being part of the side of the ink supply chamber formed within an ink supplier. The ink supply chamber is formed to have a cross-sectional area allocated in an ink flow direction so that buoyancy acting on a bubble occurring in the ink supply chamber the size of which would cause a printing defect becomes larger than drag based on an ink flow velocity in the ink supply chamber when ink is emitted from all the ink emission orifices acting on the bubble, whereby the bubble moves away from the ink inflow orifices.
A bubble that occurring in the ink supply chamber due to printing operation or the like grows because of printing operation or the like and may hinder ink supply as a result of blocking the ink inflow orifices of the individual flow passages, causing a printing defect. In the present invention, the buoyancy that moves a bubble growing to such a size as to cause a printing defect away from the individual flow passages acts larger than drag based on the flow velocity of ink that flows toward the individual flow passages from the ink supply chamber. As a result, a bubble large enough to cause a printing defect is moved away from the individual flow passages (the ink inflow orifices) by the buoyancy, so that stable printing is achieved. Therefore, an ink suck mechanism or the like need not be used to discharge bubbles by sucking ink. In other words, highly reliable printing can be performed by preventing bubble-induced printing defects with a simple structure.
According to another aspect of the present invention, the following two expressions are satisfied for a given printing rate.
[(Q/S)2xc3x97Cdxc3x97xcfx81xc3x97xcfx80xc3x97d2]/8 less than (xcfx81xc3x97gxc3x97xcfx80xc3x97d3)/6;
and
dxe2x89xa72Np
where
Q: Average ink flow quantity during printing,
S: Minimum cross-sectional area in the ink flow direction within the ink supply chamber,
Cd: Resistance coefficient,
xcfx81: Ink density,
g: Gravitational constant,
Np: Individual flow passage (ink emission orifice) pitch, and
D: Bubble diameter.
A bubble within the ink supply chamber that has at least twice (=2Np) the diameter of individual flow passage pitch is difficult to discharge from one individual flow passage by ink emission. As a result, the individual flow passage remains blocked, causing a printing defect. Therefore, by having the ink supplier and the head chip so that buoyancy [(xcfx81xc3x97gxc3x97xcfx80xc3x97d3)/6] acting on the bubble (dxe2x89xa72Np) is greater than drag [[(Q/S)2xc3x97Cdxc3x97xcfx81xc3x97xcfx80xc3x97d2]/8] produced by the flow velocity of ink that flows into the individual flow passage from the ink supply chamber, the bubble to cause the printing defect is moved away from the individual flow passage by the buoyancy. Therefore, bubble-induced printing defects can be prevented with a simple structure without having to provide a mechanism for discharging bubbles.
According to another aspect of the present invention, the ink supply chamber includes an ink tank part that communicates with the ink supply chamber and supplies ink to the ink supply chamber.
Since the ink tank part that supplies ink to the ink supply chamber is provided, an ink exchange interval is extended by supplying ink to the ink supply chamber from the ink tank part, improving the ease of use of the inkjet recording head cartridge.
According to another aspect of the present invention, a filter member intervenes between the ink supply chamber and the ink tank part.
Since a filter is provided between the ink supply chamber and the ink tank part, it can impede invasion into the head chip of foreign particles coming through the ink supply chamber from the ink tank part, increasing the reliability of printing. In other words, printing can be performed with high image quality. Moreover, since the filter member is provided, by exchanging only the ink tank part, the head can be used up to its operating life without discarding it at ink exchange.
According to another aspect of the present invention, the ink tank part is located upward in the gravity direction with respect to the ink supply chamber and holds ink in free condition.
Ink within the ink supply chamber is heated by printing operation and causes convection. Therefore, if the ink tank part is holding the ink in free condition, bubbles within the ink supply chamber are moved to the ink tank part by the convection, preventing the bubbles from growing in the ink supply chamber. As a result, the possibility that the bubbles cause a printing defect can be reduced.
According to another aspect of the present invention, an air lump of 1 mm3 or more always exists in the ink tank part.
By sealing beforehand an air lump of 1 mm3 or more in the ink tank part, bubbles occurring in the ink supply chamber are moved to the ink tank part by convection and grow integrally with the air lump within the ink tank part. In other words, it can be prevented that bubbles growing in the ink supply chamber impede ink supply from the ink tank part to the ink supply chamber.
According to another aspect of the present invention, the recording head cartridge is shipped with ink filled without bubbles existing in the ink supply chamber.
The recording head cartridge is shipped with ink filled without bubbles existing in the ink supply chamber. If a bubble exists in the ink supply chamber, when gas is deposited from the ink by printing operation or the like, the bubble already existing in the ink supply chamber grows mainly and impedes ink supply from the ink tank part to the ink supply chamber, possibly causing a printing defect. Accordingly, by shipping the recording head cartridge without bubbles existing in the ink supply chamber, bubble growth within the ink supply chamber is restrained and the above-described printing defect is prevented.
According to another aspect of the present invention, the sum of the capacity of the ink supply chamber and the initial capacity of ink in free condition in the ink tank part is greater than the total volume of ink emitted during one print job, defined in an ink temperature rise and cooling cycle in the recording head cartridge.
Ink temperature within the ink supply chamber rises because of printing operation and ink is moved to the ink tank part by convection, generating and growing a bubble. However, also in the ink supply chamber, air dissolved in the ink deposits as a bubble. Usually, the bubble dissolves in the ink again when the ink temperature has fallen after the termination of the print job. However, if printing operation is performed continuously, the bubble grows and no longer dissolves in the ink even if the ink has been cooled.
Data obtained experimentally shows that if the sum of the capacity of the ink supply chamber and the initial capacity of ink held in free condition in the ink tank part is greater than the total volume of ink emitted during one print job, air deposited by a rise in ink temperature dissolves in the ink again when the ink temperature has fallen. Therefore, the bubble generation and bubble growth in the ink supply chamber, caused by printing operation, can be restrained without fail.
According to another aspect of the present invention, the inkjet recording head cartridge includes an ink emission face on which ink emission orifices are formed, an ink supplier provided with an ink supplying chamber inside thereof; and a heater face orthogonal to the ink emission face, the heater face being part of the side of the ink supply chamber. The ink supply chamber is formed so as to have a cross-sectional area allocated in an ink flow direction so that pressure fluctuation within the ink supply chamber at the time of ink emission becomes an overattenuation mode or critical attenuation mode.
Since the ink supply chamber is formed so as to have a cross-sectional area in an ink flow direction so that pressure fluctuation within the ink supply chamber at the time of ink emission becomes an overattenuation mode or critical attenuation mode and, regardless of printing condition, it can be prevented without fail that the pressure fluctuation amplifies so that the ink refill of the ink emission orifices become imperfect, causing ink emission defects.
According to another aspect of the present invention, the inkjet recording head cartridge includes an ink emission face on which ink emission orifices are formed, an ink supplier provided with an ink supplying chamber inside thereof, and a heater face orthogonal to the ink emission face, the heater face being part of the side of the ink supply chamber. The relation of (R1+R2)2xc3x97(C1+C2)xe2x89xa74xc3x97(L1+L2) is satisfied, where L1 is the inertance of the individual flow passage, L2 is the inertance of the ink supply chamber, R1 is the resistance value of the individual flow passage, R2 is the resistance value of the ink supply chamber, C1 is the capacitance of meniscus of the ink emission orifice, and C2 is the capacitance of the ink supply chamber.
Since the present invention forms the ink supplier and the head chip so that the above-described relational expression is satisfied, for patterns of any image quality, pressure oscillation at the time of ink emission can be completely attenuated. Therefore, by appropriately designing the internal volume, cross-sectional area, and length of the ink supply chamber of the present invention, pressure fluctuation within the ink supply chamber at the time of ink emission can be attenuated without causing a bubble or communicating with the outside air, thereby providing increased printing reliability.
According to another aspect of the present invention, an ink jet recording apparatus including any of the above inkjet recording head cartridges is provided.
By mounting the inkjet recording head cartridge, without providing a special mechanism, bubble-induced printing defects, and printing defects caused by the resonance of pressure fluctuation within the ink supply chamber can be prevented. As a result, a reliable inkjet recording apparatus with a simple structure can be provided.
According to another aspect of the present invention, the inkjet recording apparatus includes: individual flow passages having each an ink emission orifice at one end thereof and an ink inflow orifice at another end; an ink supply chamber having open ink inflow orifices; an inkjet recording head cartridge having an ink tank part that supplies ink to the ink supply chamber through a filter member placed upward in the gravity direction of the ink supply chamber; a determination unit that determines whether, in one print job defined in temperature rise and cooling cycles of ink in the recording head cartridge, the total volume of ink emitted from the ink emission orifices exceeds the sum of the capacity of the ink supply chamber and the initial capacity of ink held in free condition in the ink tank part; and a printing control unit that, if the total volume of the ink exceeds the sum, halts printing during the print job, and resumes printing after the ink within the ink supply chamber is cooled to a predetermined temperature.
The ink temperature of the ink supply chamber rises because of printing operation and the ink is moved to the ink tank part by convection, generating and growing a bubble. However, also in the ink supply chamber, air dissolved in the ink deposits as a bubble. Usually, the bubble within the ink supply chamber dissolves in the ink again when the ink temperature has fallen after the termination of the print job. However, if printing operation is performed continuously, the bubble grows and does not dissolve again in the ink even if the ink has been cooled.
Accordingly, in the present invention, in the case where a determination unit determines that the total amount of emitted ink used by printing exceeds the sum of the capacity of the ink supply chamber and the initial capacity of ink held in free condition in the ink tank part, printing operation is temporarily halted to cool the ink, thereby preventing the bubble from growing to the extent that it cannot redissolve. This prevents printing defects caused by the growth of the bubble from reducing image quality.